The present invention relates to a heat sink mounting for a semi-conductor device and to a method of making the mounting. More particularly, the invention contemplates a mounting which can be disassembled for replacement of the semi-conductor device if the device does not meet quality control testing.
Heat sink mountings are commonly provided for semi-conductor devices which carry substantial current loads. High current levels can produce harmful heating of a semi-conductor device unless the heat is properly dissipated. Heat sink mountings of the type to which the present invention is directed, as shown for example in U.S. Pat. No. 4,049,185, issued Sept. 20, 1977, to Nippert, commonly include a base member having a base body for supporting the semi-conductor device on an upper surface and a downwardly extending threaded stem. The mounting is typically attached to a heat sink panel by screwing the stem into a threaded hole in the panel.
The surface upon which the semi-conductor is supported is usually defined within a recess in the top of the base body. Quite often a steel tube surrounds the recess and extends a substantial distance above the top of the base body. This steel tube may be brazed in position, as shown in U.S. Pat. No. 4,049,185, or permanently mechanically joined to the base member, as disclosed in U.S. Pat. Nos. 4,198,874 issued Aug. 3, 1965 to Doll, 3,374,014, issued Mar. 19, 1968 to Kull, and 3,918,625, issued Nov. 11, 1975 to Nippert.
The components of the semi-conductor device, assembled within the steel tube, include a semi-conductor disc, on top of which is positioned a silver disc. A contact disc attached to an upwardly extending contact shaft is positioned on the silver disc. The shaft is surrounded by an electrically non-conductive bushing which, in turn, is pushed downward by means of one or more spring washers. The spring washers are held in place by a spacer washer which is secured to the steel tube in any of several fashions. In one approach, the steel tube is crimped slightly above the washer to prevent upward movement in the tube. In another approach, tabs are punched from the side wall of the steel tube and bent inward to contact the top of the spring washer, thereby holding all of the component parts together.
After the various parts are assembled, the device is tested. If a device does not pass the inspection test, it is necessary to throw away the mounting elements along with the defective semi-conductor disc with most prior art heat sink mountings. This results in unacceptably high scrap costs, however, since the high conductivity copper from which a typical base member is formed is relatively expensive.
U.S. Pat. No. 3,025,435, issued Mar. 13, 1962, to Green discloses a heat sink mounting which includes a base member and a cylindrical tube portion. The exterior of the lower end of the tube portion and the interior of the base member recess are threaded such that the heat sink mounting may be taken apart for repair if the semi-conductor element does not operate properly. While offering the advantage that it can be disassembled, the heat sink mounting structure of the Green U.S. Pat. No. 3,025,435 requires the somewhat difficult and time consuming operation of machining threads on the elements to be joined.
Accordingly, it is seen that there is a need for a simple heat sink mounting structure for a semi-conductor device, which structure may be disassembled to permit replacement of a defective semi-conductor element.